1. Field of the Invention
This application relates broadly to bolt assemblies for firearms. More particularly, it concerns an improved form of bolt assemblies for M4/M16 military automatic and semi-automatic firearms.
2. Description of the Prior Art
The ubiquitous M4/M16 firearms are based on a gas-operated bolt assembly that includes a multi-lug bolt and a robust barrel extension with which the bolt locks and unlocks in firing each round of ammunition. The bolt assembly also includes an elongated firing pin, a spring-loaded ejector and a spring-loaded extractor configured to releasably engage a cartridge as it is placed in the firing chamber, opened up by the forward motion of the bolt just before it rotates to lock. Thus, when the rifle is fired, the interlocked bolt receives a recoil force that is transmitted from the face of the bolt to its lugs. The lugs in turn transmit the recoil force to corresponding lugs of the barrel extension. Gas impinges between the bolt and bolt carrier forcing the bolt carrier to the rear. A cam in the bolt carrier causes the bolt to unlock from the barrel extension and open up the firing chamber. As the bolt thus travels rearward, the extractor pulls the expended cartridge from the firing chamber. The cartridge is then ejected allowing chambering of another round by the bolt assembly. This process is repeated as controlled by the firearm trigger until the last cartridge in the magazine is expended.
It is well known by the U.S. Military and the military of other countries that the bolt assemblies of M4/M16 firearms are subject to failures due to the extreme stresses and temperatures to which they are subjected during use, particularly the carbine models. Those skilled in the art have described such deficiencies and proposed solutions, e.g., see U.S. Pat. No. 6,182,389 and prior art cited therein which are incorporated herein by reference. In summary, these deficiencies are (a) breakage of the bolt lugs that engage the barrel extension, (b) breakage of the bolt at the cam pin hole, (c) malfunction of the extractor causing jamming of the firearm due to a spent cartridge remaining in the firing chamber, (d) failure of the springs that bias the extractor into cartridge engagement, (e) accumulation of trash particles on the bolt face beside the ejector and under the extractor, (f) misfirings caused by the firing pin and (g) insufficient strength in the bolt per se to sustain the extreme forces to which it is subjected.
The present invention overcomes these known deficiencies in the prior known bolt assemblies of M4/M16 firearms thereby providing new and improved bolt assemblies capable of firing a remarkably greater number of rounds than previously available M4/M16 firearms.
A principal object of the invention is the provision of improved bolt assemblies for M4/M16 automatic and semi-automatic firearms.
A further object is the provision of an improved form of bolt assemblies for M4/M16 firearms that have greater service life, fewer extraction problems and an overall improvement in the reliability of the weapons that contain them.
Other objects and further scope of applicability of the present invention will become apparent from the detailed descriptions given herein; it should be understood, however, that the detailed descriptions, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent from such descriptions.
The objects are accomplished in accordance with the invention by the provision of unique improvements of prior known M4/M16 firearms that comprise:
(a) a bolt defined by a proximal end, a distal end terminating in a bolt face surrounded by an integral bolt head and an integral cylindrical portion disposed between the proximal end and the distal end along a longitudinal axis, the bolt head having a plurality of bolt lugs with walls extending integrally and radially outwardly thereof and a firing pin bore concentrically disposed in the bolt along the longitudinal axis,
(b) an extractor defined by a proximal end, a distal end and an integral central section comprising a dependent pivot pin receiving lug,
(c) a longitudinal opening in the integral cylindrical portion to receive the extractor,
(d) a proximal ledge portion within the longitudinal opening,
(e) an extractor pivot pin coupling the pivot pin receiving lug into the opening,
(f) a pair of right and left springs that bias the extractor distal end toward the bolt face,
(g) a firing pin reciprocally carried in the firing pin bore,
(h) a cam pin carried in a transverse bore in the integral cylindrical portion and retained therein by the firing pin extending through a transverse bore in the cam pin and
(i) a barrel extension defined by a proximal end, a distal end, an integral central portion and a plurality of barrel extension lugs extending integrally and radially inwardly of the barrel extension distal end to operatively engage the bolt lugs.
A first unique improvement provided by the invention is an improved extractor comprising a proximal end, a right integral lateral lug portion defining a right partial bore that receives the right spring, a left integral lateral lug portion defining a left partial bore that receives the left spring. The right and left partial bores (a) are parallel to each other, (b) comprise proximal and distal vertical ramp portions and (c) are transversely spaced so they straddle the firing pin. This paired spring configuration that straddles the firing pin substantially increases the extractor force applied to the cartridge for extraction with less spring stress. In turn, this spring configuration allows the springs to function for a much longer service life.
A second unique improvement is an improved extractor having its pivot pin receiving lug positioned at the longitudinal center of the mass of the extractor. This reduces the tendency for the rotation of the bolt to release the extractor""s grip on the cartridge case and increases the force applied by the springs in extracting cartridges.
A third unique improvement is an improved extractor having detent means to secure the extractor pivot pin in the pivot pin receiving lug and especially such a detent that comprises a ceramic ball and captive spring means to bias the ball against the extractor pivot pin. The means provides position retention of the pivot pin in the receiving lug and the combination of a ceramic ball with a rubber spring provides significantly greater force applied against the detent ball than can be achieved with a steel compression spring of the same volume.
A fourth unique improvement is that the walls of the bolt lugs are angled tangent to full radius fillets joining adjacent bolt lugs. This provides much greater strength to the lugs at their base connection to the bolt head while greatly reducing cracking and adding remarkable increase to bolt life.
A fifth unique improvement is providing that the bolt head junction with the integral cylindrical portion of the bolt is rebate filleted. This provides a larger radius at the intersection of the bolt face with the bolt head and provides a unique xe2x80x9ctrash groovexe2x80x9d to prevent particles from binding the ejector.
A sixth unique improvement is the provision of a bolt face that has a circular periphery. This increases useable life of the bolt assembly and reduces the amount of trash that is pushed past the bolt face under the extractor.
A seventh unique improvement is having the walls of the barrel extension lugs angled tangent to substantial radius fillets joining adjacent barrel extension lugs. This makes these lugs stronger and remarkably reduces the tendency of them to fail.
An eight unique improvement is the provision of a firing pin that has a diameter of between 0.116 and 0.117 inches along its portion that extends through said cam pin. This smaller firing pin diameter of the pin""s center portion allows the twin extractor springs to vertically clear. The firing pin mass is also reduced as compared with those used in accordance with the prior art to thereby reduce the available energy that causes the pin to mark the primer as the firearm chambers the round. The smaller firing pin enables the diameter of the cam pin also to be reduced. The smaller diameter cam pin allows the bolt to become stronger at the point that the cam pin receiving hole is placed in the bolt. This was an original source of bolt failures for prior known M4/M16 type firearms. In addition to reducing the diameter of the cam pin, the invention also adds a step in the cam pin that terminates in a partial spherical surface. This surface provides a stop for the cam pin to limit its travel into the bolt. The prior known M6 bolts had two stake marks pushed into them that reduced the diameter of the cam pin hole. This displaced material prevents the bolt from being assembled into the weapon incorrectly. The bolt assemblies of the present invention accomplish the same function, but provide a good transition point for the cam pin to interface with the bolt without creating any stress risers.